The present disclosure relates to continuous emulsion/aggregation (E/A) processes for coalescing particles. These processes are useful for producing toner compositions, and can be considered to be “green” processes due to their reduced energy consumption.
Toner compositions are used with electrostatographic, electrophotographic or xerographic print or copy devices. In such devices, an imaging member or plate comprising a photoconductive insulating layer on a conductive layer is imaged by first uniformly electrostatically charging the surface of the photoconductive insulating layer. The plate is then exposed to a pattern of activating electromagnetic radiation, for example light, which selectively dissipates the charge in the illuminated areas of the photoconductive insulating layer while leaving behind an electrostatic latent image in the non-illuminated areas. This electrostatic latent image may then be developed to form a visible image by depositing finely divided electroscopic toner particles, for example from a developer composition, on the surface of the photoconductive insulating layer. The resulting visible toner image can be transferred to a suitable receiving substrate such as paper.
Processes for forming toner compositions are known. For example, emulsion/aggregation (E/A) processes involve preparing an emulsion of toner ingredients such as a surfactant, a monomer, a colorant, and a seed resin in water. The monomer is polymerized to form a latex. The emulsion is then aggregated and coalesced to obtain a slurry of toner particles. This allows the particle size, particle shape, and size distribution to be controlled. Washing of the resulting product, and then isolating the toner particles, completes the process.
Current E/A processes are generally performed as batch processes. Batch processes for producing resins begin with a bulk polycondensation polymerization in a batch reactor at an elevated temperature. The time required for the polycondensation reaction is long due to heat transfer of the bulk material, high viscosity, and limitations on mass transfer. The resulting resin is then cooled, crushed, and milled prior to being dissolved into a solvent. The dissolved resin is then subjected to a phase inversion process where the polyester resin is dispersed in an aqueous phase to prepare polyester latexes. The solvent is then removed from the aqueous phase by a distillation method.
Batch processes generally require a long cycle time between batches. It can be difficult to control the particle size and circularity consistently between lots. Batches are made in volumes of thousands of gallons at a time. Malfunction of the control system during a batch E/A process can result in the entire batch not meeting specification and thus being considered waste. Also, batch processes are generally labor-intensive and require a great deal of equipment, inventory, and storage space due to their long cycle time. The use of solvents can also cause environmental concerns.
It would be desirable to provide coalescence processes that allow for the preparation of toner in a manner that is more efficient, takes less time, results in a consistent toner product, and reduces waste volumes.